Thick oil is an important constituent of hydrocarbon energy, and its characteristics are as follows:
Thick oil contains high contents of colloid and asphalt and low content of light fractions. Meanwhile, the relative density and viscosity of thick oil increase with the increase in the contents of colloid and asphalt.
The viscosity of thick oil is particularly sensitive to temperature. The viscosity decreases sharply with the increase in temperature, and such phenomenon is more significant in crude oil with higher viscosity.
Thick oil contains much heteroatom such as sulfur, oxygen and nitrogen.
The content of the paraffin in the thick oil is generally low. However, very few oil fields are the “double-high oil fields” with high contents of both asphalt and paraffin, and are characterized by having crude oil with high viscosity and high solidifying point.
The properties of crude oil in the same thick oil reservoir often vary greatly between different well sections of a vertical oil layer and between different wells on the same plane.
With the continuous development of the drilling and completion technology and oil recovery technology in horizontal wells. The horizontal wells facilitate to improve output of the single wells, increase recoverable reserves and enhance oil recovery factor. Nowadays the horizontal wells development technology is used in various oil reservoirs. For homogeneous sandstone or carbonate oil reservoirs, traditional completion methods such as open hole completion, primary screen pipe completion and perforated completion give rise to some problems in the development of horizontal wells. As the producing horizontal section is relative long, the producing pressure is uneven in the whole horizontal section due to the effect of the frictional resistance in the wellbore. The producing pressure at the heel end is the largest while the producing pressure at the toe end is the smallest, resulting in uneven fluid production in the horizontal section, and even the situation that no fluid is produced at the toe end so as to significantly affect the development effect of the horizontal wells.